Radio access technologies (e.g., GSM, UMTS, CDMA, LTE) often require that a mobile device's (e.g., mobile computer, smartphone, tablet computer, etc.) internal clock is in synch with a network provider's system clock. However, internal clocks at the mobile device are often subject to clock drift due to changes in temperature, vibration, or other environmental conditions. To correct for clock drift, wireless signals received from the network provider can include clock synchronization data that the radio access technology processor at the mobile device can use to correct the mobile device's internal clock to more closely match the network's system clock.
Global navigation satellite system technologies (e.g., GPS, GLONASS, Galileo, Beidou systems, etc.) also require that the internal clock at the mobile device is synchronized with the GNSS system clock. A small difference between the GNSS system clock and a mobile device's internal clock can result in large errors in location calculations. Because acquisition of GNSS satellites and synchronization of GNSS clocks based on GNSS signals can take a long time, often GNSS systems can take a long time to provide an accurate location for the mobile device.
The startup time of a GNSS system can be reduced and accuracy improved by assisting the GNSS system with data from the network. For example, a radio access technology processor of the mobile device can quickly acquire network radio signals and obtain clock synchronization information from the network signals. The clock synchronization information can be used to correct the clock drift associated with the GNSS processor clock within the mobile device. However, if the radio access technology processor is turned off, the GNSS system can no longer receive the benefit of network-based clock synchronization.